Goniobranchus reticulatus is a small, colourful species of sea slug in the family Chromodorididae. It is found in the western Indo-Pacific and originally described from Tongatapu, Tonga. It has a white mantle covered in a reddish reticulate pattern, with yellow edging on the foot and appendages. Several similar species occur within the G. tinctorius colour group, forming a complex of at least seven species, and the true G. reticulatus is probably not the species most commonly identified under that name. The length of the body is reported to reach 100 millimetres (3.9 in), but the original description is of an animal 27 to 34 millimetres (1.1 to 1.3 in) in length. Like other hermaphroditic gastropod molluscs, the species possesses both male and female organs, and can shed and rapidly regenerate the external portion of the penis after mating. This G. reticulatus sea slug was photographed off the coast of Anilao in the Philippines.